Throughout its 13 billion year history, the Milky Way has devoured neighbouring galaxies and stars to get to the size it is today. Now scientists believe they have discovered the largest merger in the Milky Way’s history, which experts have called the ‘Kraken’.
An international team of researchers from Germany and the US ran a computer simulation to construct the history of our home galaxy.
Specifically, the team were looking at globular clusters – large, spherical groups of stars which clump together.
These globular clusters tend to signify ancient remnants of smaller galaxies which have been absorbed by the larger Milky Way over billions of years.
Through the simulation, the team spotted evidence of five galactic mergers, with each one containing at least 100 million stars.
One in particular caught the eye of astronomers, as it had never been documented before.
It turned out to be evidence of the oldest and largest merger the Milky Way has ever experienced, according to the research published in the journal Monthly Notices of the Royal Astronomical Society.
The collision took place 11 billion years ago, when the Milky Way was four times smaller than it is today.
Study lead author Diederik Kruijssen, an astronomer at the University of Heidelberg in Germany, said: “The collision with Kraken must have been the most significant merger the Milky Way ever experienced.
“Before, it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which took place some nine billion years ago, was the biggest collision event.
“However, the merger with Kraken took place 11 billion years ago, when the Milky Way was four times less massive.
“As a result, the collision with Kraken must have truly transformed what the Milky Way looked like at the time.”
The scientists can use the findings of their study to piece together more information on the Milky Way’s family tree.
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While the collision with Kraken is significant, there are likely to be more discoveries of galactic mergers in the near future.
Mr Kruijssen said: “The debris of more than five progenitor galaxies has now been identified.
“With current and upcoming telescopes, it should be possible to find [evidence of] them all.”
However, the Milky Way is not done with its mergers.
Andromeda, the Milky Way’s nearest, and much bigger, neighbouring galaxy is headed towards us.
Andromeda is approaching the Milky Way at around five million kilometres a year, and in two to four billion years, it could consume our home galaxy.
However, humanity will not have to worry about that, as our Sun will have destroyed the solar system by that point.
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